1. Field of the Invention
Embodiments of the present invention relate generally to a method for acquiring a settling time, and more specifically, relate to a method for acquiring a settling time of a deflection amplifier for electron beam deflection in an electron beam writing apparatus, for example.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 10 is a conceptual diagram explaining operations of a variable shaping type electron beam writing or “drawing” apparatus. The variable shaping type electron beam (EB) writing apparatus operates as described below. A first aperture plate 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the X direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
When performing writing in a writing apparatus, a charged particle beam such as an electron beam is deflected by a deflector, where a DAC (digital/analog converter) amplifier is used for deflecting the beam. Beam deflection using the DAC amplifier serves, for example, for controlling the shape and size of a beam shot, controlling the position of a beam shot, and blanking of a beam. For performing the beam deflection, it is necessary to set a settling time of a DAC amplifier needed to accurately perform deflection by a set movement amount without an error. If the settling time is insufficient, an error occurs in the deflection movement amount. By contrast, if the settling time is too long, the throughput degrades. Therefore, it is desirable to set a settling time to be as short as possible within the range where no error occurs.
With high accuracy and miniaturization of circuit patterns typified by semiconductor devices in recent years, higher writing accuracy and higher throughput are also needed for an electron beam writing apparatus. Therefore, even slight positional variation of a pattern written on a desired position on the mask by beam deflection described above affects dimension accuracy in manufacturing semiconductor circuits. Thus, it is necessary to optimize the settling time described above in beam deflection using a DAC amplifier, especially with respect to control of the shot position. Conventionally, a writing position is measured by a position measuring device, and then, a settling time is set in a manner such that no positional deviation occurs within a range measurable by the position measuring device (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2010-074039).
However, with future further miniaturization and higher accuracy, it is becoming difficult to achieve highly accurate evaluation of the settling time by the method described above.